Ex-Google TechLead explains the interview process at Facebook for staff software engineer. (FYI, this video is a little more technical in nature.)
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Video Transcript
(Note: This transcript is auto-generated by YouTube and may not be 100% accurate.)
00:00
hey welcome back to coffee time with
00:01
your host X Google X Facebook tech lead
00:03
and it occurred to me that I never
00:05
really explained how I got my job at
00:07
Facebook as a staff software engineer
00:09
making five hundred thousand dollars per
00:11
year
00:11
today I thought I would tell you about
00:13
how that interview process went I landed
00:15
this offer about one and a half years
00:17
ago when I was working over at Google as
00:19
a tech lead I might remind you before
00:22
all the drama about my wife leaving me
00:24
happened before I became unemployable
00:26
for bashing Facebook but this may be a
00:28
path that you would like to pursue as
00:30
well at some point in your future maybe
00:32
not now maybe not ever really I wanted
00:35
to explain why might even give you an to
00:37
survive if you know the information if
00:39
you know knowledge if you can pass these
00:40
interviews you should be qualified for
00:42
the job it would otherwise be like
00:44
saying students I say Harvard somehow
00:46
have some secret bit of information that
00:49
is non-public and then they only tell
00:50
that information to their friends and
00:52
then only those people are able to get
00:53
into Harvard and I feel that this
00:55
information disparity is not fair it's
00:57
not fair for people who don't have those
00:59
professional network connections who may
01:01
be from underprivileged communities so
01:03
that's my perspective about giving you
01:05
guys as much information as you can to
01:07
pass these coding interviews
01:08
all right so Facebook generally has
01:10
three different types of interviews you
01:12
can usually tell which one you may be at
01:13
they have coding systems design and
01:16
behavior so the coding focuses on just
01:19
your average sale each code the type of
01:21
questions and what you have to solve
01:22
some coding exercise and that's really
01:24
what's a I'll go pro which I talked
01:26
about it's going to help you get through
01:27
and a lot of junior engineers they
01:29
stumble on this portion or they just
01:31
miss out on a lot of these problems the
01:33
systems design interview is not so
01:35
focused on coding and in fact they'll
01:36
probably get a little bit mad if you
01:38
start coding too much they want you to
01:39
talk about how these pieces of code
01:41
interact with each other and that
01:43
overall architecture of it and then
01:45
there's the behavior portion in which
01:47
they tend to value your ability to
01:48
handle conflict build consensus lead
01:51
projects push impact and overall have
01:53
good collaboration and communication
01:54
skills because overall programming is a
01:57
team sport for myself since I was
01:59
interviewing for a senior role I had one
02:01
coding question two systems design
02:03
interviews and then one behavioral
02:05
portion and in each of these they
02:06
generally do continue to ask you some
02:08
coding questions so it's not like they
02:10
just ask you one let me tell you about
02:11
the coding questions that I had though
02:13
and there's a good thing I took notes on
02:15
these so I can tell you the exact
02:16
questions I was asked and you can think
02:18
about how you may solve some of these as
02:20
well you can just pause the video as we
02:22
go along here the first question is
02:24
given to duplicate binary trees so you
02:27
got tree a and three B and you're given
02:30
a node and tree a find that same
02:32
corresponding node in those B so you can
02:35
think about how you may solve this by
02:37
remember my approach was I would try to
02:39
traverse one tree find the note and then
02:41
traverse the second tree and see if I
02:43
can find that same note but then I
02:45
realized that there was no good way to
02:47
compare the two nodes the interviewer
02:49
kind of stopped me at that point I had
02:51
to step back and think about it and the
02:53
ultimate approach which I think is the
02:55
right one is to just reverse both at the
02:56
same time and when you reach the node in
02:59
a then you know you've reached that same
03:00
node in the second binary tree as well
03:03
but the main trick here is that even
03:05
though most people may have been taught
03:06
to traverse one binary tree at a time
03:08
doing both treat reversals at the same
03:11
time sort of test your mastery of this
03:13
area now the funny thing is for a
03:15
standard interview I think this would be
03:16
the only question but I actually ended
03:18
up solving like three questions in the
03:20
single session so the second question
03:22
they asked was given an array like one
03:25
zero zero two five zero move all of the
03:27
zeros to the right to the end of the
03:29
array and again this isn't necessarily
03:32
so difficult but the challenge is to do
03:34
it in like a single pass linear time
03:36
algorithm make it very efficient and
03:38
come up with the proper time space
03:40
analysis and one brute force technique
03:42
is you can go through the array find the
03:45
first zero and move it to the end go
03:46
through the array find the next zero
03:47
move it to the end and you just keep
03:49
moving these values and that's probably
03:51
going to take quadratic time n square
03:53
time because you got to go through n
03:55
iterations and for each iteration you
03:57
may have to shift and more elements the
03:59
more optimal solution can be done in
04:01
linear time and constant space you keep
04:03
in the index to the last item in the
04:05
array and anytime you find the zero you
04:07
just swap that element with the last
04:09
item and then you move that last index
04:11
one left and you just keep going like
04:13
that and then you can process through
04:15
the whole range it's a pretty ridiculous
04:17
question but you just got to play that
04:18
game
04:19
the next question is check of a string
04:21
of parentheses valid a very common
04:23
question you always get asked this type
04:25
of thing you can either solve that using
04:27
like a
04:27
Hunter but if there are multiple
04:29
different types of parentheses then you
04:30
can use like a stack and when you
04:32
encounter and open the in parentheses
04:34
you push that on to the stack we
04:35
encounter a closing parenthesis you pop
04:37
that off of the stack and you check that
04:39
they match and then there's a follow-up
04:41
question which was to remove all
04:42
unbalanced parentheses another question
04:45
was you're given two binary strings and
04:47
you need to add them manually
04:48
essentially just do a duration using a
04:50
carryover variable that can be done in
04:52
linear time constant space and we go
04:54
over a question similar to this over an
04:56
algo Pro except that they're linked
04:58
lists instead so it's a little bit
04:59
trickier that way and then the last
05:01
question is you are given an array of
05:03
objects small medium and large and that
05:05
you have to sort them in place and you
05:08
know this was a mix of using the proper
05:10
data structures because they weren't
05:11
numbers there's like small medium and
05:13
large objects in there and then coming
05:15
up with the algorithm to sort this
05:17
efficiently the optimal algorithm would
05:19
use no space and it would be linear time
05:21
just do the entire sort in one iteration
05:24
one past I remember the original
05:26
approach I did was first I had a bucket
05:28
of small items and then medium and large
05:30
items combined and I would first go
05:32
through in one pass and move all the
05:34
small items to the beginning and then
05:36
we'll go through a second pass I move
05:37
all the large items to the end and just
05:39
sort the medium and large items so this
05:41
is actually a two pass algorithm so that
05:43
covers the coding and all software
05:45
engineers jr. through senior needs a
05:47
known coding you're gonna be smoked on
05:48
this no matter what level you're at
05:50
which is why it's important to keep your
05:52
skill sharp with algo procom now the two
05:55
systems design questions I got were both
05:57
pretty similar and it's totally going to
05:59
depend on the area that you're in right
06:01
for me I'm an iOS mobile developer so it
06:04
was about building an iOS app
06:05
specifically it was number one design a
06:08
flight booking app and number two design
06:10
a simple version of Instagram so both of
06:12
these questions are about having
06:14
multiple pages or surfaces in an app
06:16
there could be dozens of teams working
06:18
on these and then architecting the app
06:20
structure in the way that multiple
06:21
people can be working on this and then
06:23
handling things like caching offline
06:25
usage event navigation scroll
06:27
performance layout removing inter
06:29
dependencies between different pages for
06:31
the flight booking application the idea
06:33
is that you first search for a set of
06:34
flights you see a list you choose a
06:36
flight and then you can buy the flight
06:37
similarly for the Instagram one is like
06:40
you
06:41
have a bunch of photos then you can
06:42
click on the photo you see the details
06:44
and it's like a two-page app you can
06:47
really go in any direction that you want
06:48
in these systems design interviews is
06:50
super open for me the areas I drove into
06:53
talking more about we're handling
06:54
offline usage scenarios how do you catch
06:57
that stuff
06:58
separating dependencies between surfaces
07:00
so for example the flight booking app
07:02
you may have a payments team that is
07:04
handling the payment view for buying the
07:06
airplane ticket but then you have
07:08
another team that's handling search and
07:10
then another team that handles
07:11
displaying the list of flights and it's
07:14
like how do you structure the
07:15
application in a way such that all of
07:17
these can be independent of one another
07:19
and yet they're able to function
07:20
together and here I will talk about
07:22
having different event handlers
07:24
separating modules out such that they're
07:26
not dependent upon one another and
07:28
coming up with that module dependency
07:29
graph and I had to sort of back step
07:31
they're taking their feedback and during
07:33
the interview I actually realized an
07:35
even better architectural solution that
07:37
we hadn't figured out over at Google
07:38
that Facebook had been implementing and
07:40
they probably just appreciated that I
07:43
was able to collaborate with them to
07:44
solve that right there and then there
07:46
are also questions about holistically
07:48
structuring the app in a way that could
07:50
be suitable for both offline and online
07:52
use and then making the right
07:53
abstractions that say the network layer
07:55
and then I also talked about the UI as
07:57
well so that covers what a mobile
07:59
systems design interview may look like
08:01
for a web it will probably be very
08:02
different for example they'll probably
08:04
be about load balancers databases
08:06
master-slave replication sharding CD ins
08:09
and all of that I think what really
08:11
helped me though was really being more
08:12
interested in other parts of the code
08:14
base rather than whatever I have been
08:16
assigned right like usually people are
08:18
saying to work on one small feature and
08:19
they never take a step back and look at
08:21
how their feature interacts with
08:23
everything else and get an overview of
08:25
the entire code base that they're
08:26
working on if you can take a step back
08:29
and take a look at that that could
08:30
prepare you well for any systems design
08:32
interview that may be coming your way at
08:34
some point maybe now or in the future
08:36
and then lots of other the behavior
08:39
questions which we cover in far more
08:40
depth over in our other program Tech
08:43
interview program where we covered the
08:44
entire interview process start to finish
08:47
but the behavioral questions they really
08:49
dig and they don't accept your first
08:52
answer in fact they're trained not to so
08:54
if they ask you like what
08:55
the most challenging part about this and
08:56
you give some shallow answer like oh
08:58
yeah working with this person and then
09:00
it overcame this challenge they know
09:02
that that first answer
09:03
it's probably like a BS answer that you
09:05
have prepared so they really dig deep
09:06
and this is where it helps to really
09:09
have good examples
09:10
I prepared a number of stories myself
09:11
about the only with conflict tough
09:13
situations at work and I think that for
09:15
this area it also helps you just have
09:16
some good concrete examples which is
09:19
another reason that in whatever role
09:21
you're in it still helps to be pushing
09:23
yourself challenging yourself to do more
09:25
such that it can be something you can
09:26
talk about as you're interviewing for
09:28
your future roles so there you have it I
09:30
remember leaving the interview feeling
09:31
quite positive about it and then two
09:33
weeks later I would receive the offer
09:34
five hundred thousand dollar salary and
09:36
there was still kind of a hard decision
09:38
for me to leave Google to take up that
09:40
offer because I was quite comfortable
09:42
over at Google in fact I felt I was
09:44
probably getting a little bit too
09:45
comfortable just sitting back the idea
09:47
of learning a whole new codebase new
09:49
technologies it just seemed really
09:51
exciting to me at the time so I made
09:52
that switch turned out later to be one
09:55
of the biggest mistakes of my life but
09:57
that's another story
09:58
so that good for me it was a little bit
10:01
more of a technical video but I gotta
10:03
keep my street cred up as the tech lead
10:04
if you liked the video give it a like
10:06
and subscribe and I'll see you next time
10:08
Thanks bye